Also most states require at the minimum that a bullet be 60 grains or heavier that produces atleast 1000 ft lbs at the muzzle to be legal and /or ethical for deer.
But in some cases I dont think that is correct but they do it because it covers a wider margin of minimum calibers. Why i dont think that is a correct way to lay the law for limiting calibers for deer hunting is because I have killed a few deer with pistol calibers the 357 mag with a 158 grain hornady XTP which has about 500 lbs of muzzle energy, The 45 ACP with a 185 grain barnes XPB which has about 400 lbs of muzzle energy and a 45 long colt with a speer 260 grain JHP which has about 500 lbs of muzzle energy which have proved to be fine on deer and had plenty of penetration but ofcourse all the shots were less then 50 yards. I think it come down to this on larger calibers the muzzle energy doesnt play as big of a role as it does in smaller calibers as Jeff Cooper always said " You cannot replace bullet mass with velocity" basically that means just because a .223 has the same muzzle energy as a 44 magnum it doesnt mean the 223 is just as powerful as the 44 mag the 44 mag is a proven deer caliber time and time again but the 223 is very doubtful as being suited for deer.